Non-flammable nonaqueous electrolyte solution and lithium ion cell using same

Abstract

Disclosed are a non-flammable nonaqueous electrolyte solution and a lithium ion cell using the electrolyte solution. The non-flammable nonaqueous electrolyte solution comprises a ternary or higher-order compound additive, a high concentration of lithium salt and a phosphoric ester serving as a primary solvent. The lithium ion cell comprises a positive electrode containing a lithium transition metal oxide capable of absorbing and releasing lithium, a negative electrode containing a carbon-based material capable of absorbing and releasing lithium, and the above non-flammable nonaqueous electrolyte solution. The ternary or higher-order compound additive contains at least one compound selected from each of the three compound groups consisting of: a compound group (a) of vinylene carbonate compounds; a compound group (b) of vinyl acetate compounds, alkyl methyl carbonate compounds and vinyl ethylene carbonate compounds; and a compound group (c) of 2-pyrrolidinone compounds, cyclic alkyl compounds and cyclic pentanone compounds. The non-flammable nonaqueous electrolyte solution of the present invention can provide enhanced charge/discharge characteristics to a lithium ion cell.

1. A non-flammable, nonaqueous electrolyte solution having a lithium salt dissolved in a solvent containing a phosphate ester, comprising at least one additive compound selected from each of the three compound groups consisting of:
 (a) vinylene carbonate compounds represented by formula (I): 
 
       
         
           
           
               
               
           
         
          wherein R 1  and R 2  each independently represents a hydrogen atom or a straight-chain or branched-chain alkyl group having 1 to 4 carbon atoms, 
         (b) a compound selected from the groups consisting of vinyl acetate compounds represented by formula (II), alkyl methyl carbonate compounds represented by formula (III), and vinyl ethylene carbonate compounds of formula (IV): 
       
       
         
           
           
               
               
           
         
          wherein R 3 , R 4  and R 5  each independently represents a hydrogen atom or a straight-chain or branched-chain alkyl group having 1 to 4 carbon atoms, 
       
       
         
           
           
               
               
           
         
          wherein R 6  represents a hydrogen atom or a straight-chain or branched-chain alkyl group having 1 to 4 carbon atoms, 
       
       
         
           
           
               
               
           
         
          wherein R 7 , R 8 , R 9 , R 10 , R 11  and R 12  each independently represents a hydrogen atom or a straight-chain or branched-chain alkyl group having 1 to 4 carbon atoms; and 
         (c) a compound selected from the group consisting of 2-pyrrolidinone compounds represented by formula (V), cyclic alkyl compounds represented by formula (VI), and cyclic pentanone compounds represented by formula (VII): 
       
       
         
           
           
               
               
           
         
          wherein R 13  represents a hydrogen atom or a straight-chain or branched-chain alkyl group having 1 to 4 carbon atoms, 
       
       
         
           
           
               
               
           
         
          wherein R 14  represents a straight-chain or branched-chain alkylene group having 2 to 4 carbon atoms, 
       
       
         
           
           
               
               
           
         
          wherein R 15  represents a straight-chain or branched-chain alkylene group having 1 to 3 carbon atoms; 
         wherein each of compounds (a), (b), and (c) is present in an amount from 1 to 12% by weight and the total amount of compounds (a), (b), and (c) is from 5 to 20% by weight; 
         and further wherein the total concentration of the lithium salt in the phosphate ester-based solvent is in the range of 1.5 to 2.5 mol/dm 3 ; 
         and further wherein the solvent comprises a phosphate ester selected from the group consisting of the chain phosphate esters of formula (IX) and the cyclic phosphate esters of formula (X), wherein at least either one of the chain phosphate ester represented by formula (IX) and the cyclic phosphate ester represented by formula (X) is contained in the phosphate ester-based solvent in an amount ranging from 50 to 100% by volume: 
       
       
         
           
           
               
               
           
         
          wherein R 16 , R 17  and R 18  each independently represents an alkyl group having 1 or 2 carbon atoms, in which each of the hydrogen atoms may be substituted with fluorine, 
       
       
         
           
           
               
               
           
         
          wherein R 19  represents an alkyl group having 1 or 2 carbon atoms in which each of hydrogen may be substituted with fluorine, and R 20  represents an alkylene group having 2 to 4 carbon atoms. 
       
     
     
       2. The non-flammable nonaqueous electrolyte solution of  claim 1 , wherein the lithium salt is at least one compound selected from the group consisting of lithium salts of an inorganic acid formed from a lithium ion and an anion selected from PF 6  and BF 4 , and lithium salts of an organic acid formed from a lithium ion and an anion of formula (VIII): 
       
         
           
           
               
               
           
         
       
       wherein m and n each independently represent an integer selected from 1, 2, 3, or 4. 
     
     
       3. The non-flammable nonaqueous electrolyte solution of  claim 1 , wherein the phosphate ester-based electrolyte solution comprises a chain phosphate ester having formula (IX), and at least one cyclic phosphate ester having formula (X): 
       
         
           
           
               
               
           
         
          wherein R 16 , R 17  and R 18  each independently represents an alkyl group having 1 or 2 carbon atoms, in which each of the hydrogen atoms may be substituted with fluorine, 
       
       
         
           
           
               
               
           
         
          wherein R 19  represents an alkyl group having 1 or 2 carbon atoms in which each of hydrogen may be substituted with fluorine, and R 20  represents an alkylene group having 2 to 4 carbon atoms. 
       
     
     
       4. The non-flammable nonaqueous electrolyte solution of  claim 1 , wherein the phosphate ester-based electrolyte solution further comprises at least one compound selected from the group consisting of carbonate-based compounds, lactone-based compounds, ether-based compounds, sulfolane-based compounds and dioxolan-based compounds. 
     
     
       5. A lithium ion cell comprising:
 an electrolyte solution consisting of the non-flammable nonaqueous electrolyte solution of  claim 1 ; 
 a positive electrode containing a lithium transition metal oxide capable of absorbing and releasing lithium; and 
 a negative electrode containing a carbon-based material capable of absorbing and releasing lithium.